FORMAT



DCP Digital Cinema Package

A Digital Cinema Package (DCP) is a collection of all the relevant digital audio and video files and metadata used for the delivery and presentation of a feature film to a digital cinema.

The structure of a DCP is specified by the Digital Cinema Initiative (DCI).

The DCI provides guidelines on the format and properties of the individual elements within a DCP. An essential part of this specification is that the image information is stored in a DCP as a single JPEG2000 encoded sequence which has a 12-bit colour depth and is converted into XYZ colour space. The JPEG2000 conversion is progressive so it is frame-based. The digital video can only have two aspect ratios in 2K or 4K.

If a movie has an aspect ratio of 1:1.85, this is called ‘FLAT’. It will have an image resolution of 1998x1080 pixels (2K) or 3996x2160 pixels (4K). If the film has an aspect ratio of 1:2.39 then this is called ‘SCOPE’ (or Cinemascope) and will have an image resolution of 2048x858 pixels (2K) or 4096x1716 pixels (4K). Other formats or resolutions are not allowed.


If you want to deliver HD content (1920x1080 and an aspect ratio of 1:1.78) as a DCP at a movie theatre, the image content needs to be embedded in a FLAT image container. This means that black bars need to be inserted to the left and right of the HD image. This process is known as ‘Pillarboxing’.

Frame rates are also defined in the DCP standard. The “old” original ‘InterOp’ DCP standard introduced in 2003 allows only 24 and 48fps in 2K, and 24fps in 4K. The "new" SMPTE standard introduced in 2006, permits 24, 25, 30, 48, 50 and 60fps in 2K and 24, 25 and 30fps in 4K.
Because of the very diverse hardware found worldwide in cinemas, it is possible that there are still old JPEG2000 cinema servers in operation that only support DCPs mastered to the InterOp Standard even though this InterOp standard has long been replaced by the SMPTE standard. If one wants to show a TV production in a cinema and avoid the conversion of 25 to 24fps, you should consider whether a SMPTE 25fps DCP is compatible with the DCP server installed in the cinema.
Audio can be stored in up to 16 discrete channels, i.e. single mono WAV tracks. The sound is stored uncompressed in 24-bit audio samples with a 48 or 96kHz sampling rate. A DCP can contain multiple language versions and corresponding audio tracks in the DCP must be available for the respective language versions. Both the video and the audio information is packaged as MXFs and stored in the DCP. Subtitles are also contained in the DCP and it is possible to store multiple subtitle versions within the DCP. Subtitles, as XML files, must be formatted in the CineCanvas or SMPTE 429-5 format.

A DCP with its various elements is organised by a CPL file, a ‘Composition Playlist’. In this CPL is information about the video, audio and subtitle versions and specifies what combinations can be played. The structure and nature of the name of a CPL is defined by the Digital Cinema Naming Convention from which a text string that describes a particular CPL for a particular version of a movie can be derived. This text string contains a whole raft of information about the technical parameters of that film. More information can be found at www.isdcf.com/dcnc/.

DCPs can also be encrypted to protect the contents from unauthorised access and a multi-level encryption method is used. The media files are symmetrically encrypted using a 128-bit AES key. The decryption keys are also encrypted but this time with an asymmetrical 2048-bit AES key. The advantage of asymmetric methods is that the decryption key – known as a ‘private key’ – is not transferred but is already securely located within the projection system. A matching ‘public key’ is shared with the distributor who can then create Key Delivery Messages (KDMs) which control access to the encrypted content for each projection system. This means that DCPs for each projector are specifically encrypted and cannot be played on any other projector, other than the projector for which that particular DCP is intended. The public key, and a pre-adjustable period of validity for showing the movie, are located in the KDM.


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